1. Field of the Invention
The present invention relates to a solenoid valve driving circuit in which, after a first voltage is impressed on the solenoid coil of a solenoid valve for driving the solenoid valve, a second voltage is impressed on the solenoid coil and the driven state of the solenoid valve is maintained, as well as to a solenoid valve having such a solenoid valve driving circuit.
2. Description of the Related Art
Conventionally, it has been widely practiced to arrange a solenoid valve within a fluid passage, and by impressing a voltage on a solenoid coil of the solenoid valve from a solenoid valve driving circuit, the solenoid valve is energized to open and close the fluid passage. In this case, after the solenoid valve is driven by impressing a first voltage on the solenoid coil of the solenoid valve from the solenoid valve driving circuit, the driven state of the solenoid valve is maintained by impressing a second voltage on the solenoid coil from the solenoid valve driving circuit.
Recently, it has been desired that the driven state be maintained with low power consumption. In Japanese Patent No. 3777265 and Japanese Laid-Open Patent Publication No. 2006-308082, it has been proposed that, within a time period during which the driven state is maintained, and as a result of controlling conduction between the power source and the solenoid coil by means of a switch, energization and deenergization of the solenoid coil is carried out repeatedly, so that the driven state of the solenoid valve can be maintained with a lower level of power consumption.
Incidentally, the current flowing through the solenoid coil tends to vary over time as a result of various factors, such as changes in electrical resistance in the solenoid coil induced by temperature changes of the solenoid coil, timewise changes of the power source voltage (first voltage and second voltage) impressed on the solenoid coil from the DC power source through the solenoid valve driving circuit, and due to vibrations or shocks and the like, which are imparted to the solenoid valve from the exterior thereof. Owing thereto, within the time period during which the driven state of the solenoid valve is maintained, so as to prevent the above-mentioned various factors from occurring and causing stoppage of the solenoid valve, a current, which takes into consideration the aforementioned various factors, is superimposed on the minimal required current for maintaining the driven state. Accordingly, even when the above-mentioned various factors do not occur, the current taken in consideration of these factors still flows through the solenoid coil, and hence, electrical power savings of the solenoid valve driving circuit and the solenoid valve cannot be promoted.
Further, as a result of the current that flows through the solenoid coil being large, when driving of the solenoid valve is halted after maintaining the driven state, the solenoid valve cannot be stopped in a short time period.
Moreover, in the case that a plurality of DC power sources, having different power source voltages, are prepared and utilized on the side of users of the solenoid valves, on the manufacturer's side, even if there are solenoid valve driving circuits and solenoid valves having roughly the same capability with respect to opening/closing the same fluid passage, because it is necessary to separately manufacture the solenoid valve driving circuits and solenoid valves corresponding to differences of the various power source voltages, manufacturing costs tend to rise.
Still further, because the electrical power consumption of a solenoid valve driving circuit and a solenoid valve corresponding to the case of a relatively high power source voltage (e.g., 24V) is larger than the electrical power consumption of a solenoid valve driving circuit and a solenoid valve corresponding to the case of a relatively low power source voltage (e.g., 12V), on the side of a user equipped with a DC power source having a relatively high power source voltage, electrical power savings of the solenoid valve driving circuit and the solenoid valve cannot be achieved.